1 /* 2 * Copyright (c) 2001, 2015, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #ifndef SHARE_VM_MEMORY_FREELIST_HPP 26 #define SHARE_VM_MEMORY_FREELIST_HPP 27 28 #include "gc/cms/allocationStats.hpp" 29 30 class CompactibleFreeListSpace; 31 32 // A class for maintaining a free list of Chunk's. The FreeList 33 // maintains a the structure of the list (head, tail, etc.) plus 34 // statistics for allocations from the list. The links between items 35 // are not part of FreeList. The statistics are 36 // used to make decisions about coalescing Chunk's when they 37 // are swept during collection. 38 // 39 // See the corresponding .cpp file for a description of the specifics 40 // for that implementation. 41 42 class Mutex; 43 44 template <class Chunk_t> 45 class FreeList VALUE_OBJ_CLASS_SPEC { 46 friend class CompactibleFreeListSpace; 47 friend class VMStructs; 48 49 private: 50 Chunk_t* _head; // Head of list of free chunks 51 Chunk_t* _tail; // Tail of list of free chunks 52 size_t _size; // Size in Heap words of each chunk 53 ssize_t _count; // Number of entries in list 54 55 protected: 56 57 #ifdef ASSERT 58 Mutex* _protecting_lock; 59 void assert_proper_lock_protection_work() const; 60 #endif 61 62 // Asserts false if the protecting lock (if any) is not held. 63 void assert_proper_lock_protection() const { 64 DEBUG_ONLY(assert_proper_lock_protection_work()); 65 } 66 67 void increment_count() { 68 _count++; 69 } 70 71 void decrement_count() { 72 _count--; 73 assert(_count >= 0, "Count should not be negative"); 74 } 75 76 public: 77 // Constructor 78 // Construct a list without any entries. 79 FreeList(); 80 81 // Do initialization 82 void initialize(); 83 84 // Reset the head, tail, and count of a free list. 85 void reset(); 86 87 // Declare the current free list to be protected by the given lock. 88 #ifdef ASSERT 89 Mutex* protecting_lock() const { return _protecting_lock; } 90 void set_protecting_lock(Mutex* v) { 91 _protecting_lock = v; 92 } 93 #endif 94 95 // Accessors. 96 Chunk_t* head() const { 97 assert_proper_lock_protection(); 98 return _head; 99 } 100 void set_head(Chunk_t* v) { 101 assert_proper_lock_protection(); 102 _head = v; 103 assert(!_head || _head->size() == _size, "bad chunk size"); 104 } 105 // Set the head of the list and set the prev field of non-null 106 // values to NULL. 107 void link_head(Chunk_t* v); 108 109 Chunk_t* tail() const { 110 assert_proper_lock_protection(); 111 return _tail; 112 } 113 void set_tail(Chunk_t* v) { 114 assert_proper_lock_protection(); 115 _tail = v; 116 assert(!_tail || _tail->size() == _size, "bad chunk size"); 117 } 118 // Set the tail of the list and set the next field of non-null 119 // values to NULL. 120 void link_tail(Chunk_t* v) { 121 assert_proper_lock_protection(); 122 set_tail(v); 123 if (v != NULL) { 124 v->clear_next(); 125 } 126 } 127 128 // No locking checks in read-accessors: lock-free reads (only) are benign. 129 // Readers are expected to have the lock if they are doing work that 130 // requires atomicity guarantees in sections of code. 131 size_t size() const { 132 return _size; 133 } 134 void set_size(size_t v) { 135 assert_proper_lock_protection(); 136 _size = v; 137 } 138 ssize_t count() const { return _count; } 139 void set_count(ssize_t v) { _count = v;} 140 141 size_t get_better_size() { return size(); } 142 143 size_t returned_bytes() const { ShouldNotReachHere(); return 0; } 144 void set_returned_bytes(size_t v) {} 145 void increment_returned_bytes_by(size_t v) {} 146 147 // Unlink head of list and return it. Returns NULL if 148 // the list is empty. 149 Chunk_t* get_chunk_at_head(); 150 151 // Remove the first "n" or "count", whichever is smaller, chunks from the 152 // list, setting "fl", which is required to be empty, to point to them. 153 void getFirstNChunksFromList(size_t n, FreeList<Chunk_t>* fl); 154 155 // Unlink this chunk from it's free list 156 void remove_chunk(Chunk_t* fc); 157 158 // Add this chunk to this free list. 159 void return_chunk_at_head(Chunk_t* fc); 160 void return_chunk_at_tail(Chunk_t* fc); 161 162 // Similar to returnChunk* but also records some diagnostic 163 // information. 164 void return_chunk_at_head(Chunk_t* fc, bool record_return); 165 void return_chunk_at_tail(Chunk_t* fc, bool record_return); 166 167 // Prepend "fl" (whose size is required to be the same as that of "this") 168 // to the front of "this" list. 169 void prepend(FreeList<Chunk_t>* fl); 170 171 // Verify that the chunk is in the list. 172 // found. Return NULL if "fc" is not found. 173 bool verify_chunk_in_free_list(Chunk_t* fc) const; 174 175 // Printing support 176 static void print_labels_on(outputStream* st, const char* c); 177 void print_on(outputStream* st, const char* c = NULL) const; 178 }; 179 180 #endif // SHARE_VM_MEMORY_FREELIST_HPP